Am 28.04.2013 07:21, schrieb Hilmy Hashim:
Hello all,
This query is about a discrepancy between projection results using the *Custom
CRS Test* and *on-the-fly* transformation, and not about RSO per se.
The Proj4 parameters for GDM2000 / Peninsula RSO (EPSG:3375) as given by
epsg_tr.py (GDAL 1.9.2) are:
+proj=omerc +lat_0=4 +lonc=102.25 +alpha=323.0257964666666 +k=0.99984
+x_0=804671 +y_0=0 +gamma=323.1301023611111 +ellps=GRS80 +units=m +no_defs
This Malaysian projection requires the +no_off or *+no_uoff* flag (both
works) for rotation at the natural origin as of proj 4.8. To test, I
created a custom CRS based on GDM2000 / Peninsula RSO adding this flag.
However, there seems to be some discrepancy between the on-the-fly derived
results and the Test in the Custom CRS definition dialog.
I set the project CRS as the custom CRS I created and added the test point
in WGS84.
Test points: *1.827764875* deg N, *103.640259872222* deg E (WGS84 EPSG:4326)
Expected results: Northing *202,122.062* m, Easting *627,096.132* m
(EPSG:3375)
*The test points and projected coordinates are taken from the GDM2000
Technical Manual published by the Department of Survey and Mapping Malaysia.
*
*Test results (standard EPSG:3375)*:
cs2cs — -240332.04, 958936.71
QGIS Master (13d35ac) On-the-fly derived: Y = -240,332.0326, X =
958,936.7057
QGIS Master (13d35ac) Custom CRS Test:* -240,332.0326* N, *958,936.7057* E
QGIS 1.8 On-the-fly: projected coordinates not derived
QGIS 1.8 Custom CRS Test: -240,332.0326 N, 958,936.7057 E
*Test results (with +no_off flag)*:
cs2cs — 202122.06, 627096.13
QGIS Master (13d35ac) On-the-fly derived: Y =* -240,332.0326*, X = *
958,936.7057*
QGIS Master (13d35ac) Custom CRS Test: *202,122.0625* N, *627,096.1317* E
QGIS 1.8 On-the-fly: projected coordinates not derived
QGIS 1.8 Custom CRS Test: 202,122.0625 N, 627,096.1317 E
It looks like the Custom CRS Definition Test dialog is giving the correct
result, but the on-the-fly transformation is ignoring the +no_off flag.
Is the on-the-fly transformation using a different transformation process
and reading the proj4 parameters differently, or am I going about this
wrongly?
I made some tests with the similar Michigan omerc projections and ran
into the same problem:
http://trac.osgeo.org/gdal/ticket/4910
It looks like it is a GDAL problem.
HTH,
André Joost
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